In the headrest support structure described in patent document 1, a headrest guide, to which a headrest stay is coupled, is supported such that it can tilt in an anteroposterior direction with respect to a headrest bracket disposed on a frame of a seatback, and the headrest guide is energized backward by a spring. In this structure, the natural frequency of the headrest is freely set by changing the spring constant of the spring to ensure that the headrest does not resonate with the seatback, and the headrest is made to function as a dynamic damper with respect to vibration of the seatback to reduce vibration of the seat.    Patent Document 1: Japanese Examined Utility Model Application Publication No. 3-13377